Certain sensors, in particular light sensors, which are used for the automatic control of the driving lights and other light sources in motor vehicles, are conventional. This automatic control is meant to assist the driver who forgets to turn on the driving lights when starting off in the dark, for instance, in towns with street lighting. This is to ensure an automatic activation of the light when dusk falls, when entering a tunnel or other dark stretches. In particular, when corresponding signals or criteria from a single or a plurality of sensor elements are present is reliable activation and deactivation of the driving light to be ensured. Such criteria are, for example, information about the ambient light from a light sensor, information about the ambient dampness from a rain sensor, or information from an interval time signal of a front wiper.
From the viewpoint of safety, it is especially important that a driving light not be turned off accidentally after having been turned on correctly, i.e., that it is turned off in a driving situation where the light should not have been turned off. This risk exists, for instance, if the data processing and data transmission are unsatisfactory. Furthermore, it is important that the driving light not be turned on inadvertently, for instance, in bright daylight or in shady stretches of only brief duration. All of this is to be implementable even without providing a switch-on delay, which is disadvantageous when entering long tunnels. Especially when entering such tunnels must the light be turned on as quickly as possible since the driver's pupils have not yet widened because of the sudden onset of darkness and the driver therefore has poor vision.
The use of a rain sensor for motor vehicles as sensor for measuring the ambient brightness is described in this context in German Published Patent Application No. 100 05 127. The signal resulting from this measurement is suitable for controlling a lighting system of a motor vehicle, for example.
Furthermore, German Published Patent Application No. 196 30 216 mentions a vehicle having a light control that is a function of the driving situation. A control unit activates a driving light whenever the brightness detected by an ambient light sensor drops below an associated first brightness threshold value and the brightness recorded by a driving-direction-specific light sensor is below an assigned second brightness threshold value.
Furthermore, European Published Patent Application No. 0 997 359 describes an integrated self-test for rain sensors. In this case, a test signal is generated, which is compared to a measuring signal.
European Published Patent Application No. 1 027 227 describes a device for controlling a lighting device. Utilized for the control are an optical sensor on the one hand, and a water sensor on the other.